© 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ITE PC v4.0 Chapter 1 1 Static Routing Routing Protocols and Concepts – Chapter 2

ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public General Role of the Router  Functions of a Router Best Path Selections Forwarding packets to destination  Introducing the Topology series routers connected via WAN links Each router connected to a LAN represented by a switch and a PC

ITE PC v4.0 Chapter 1 3 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Routing and Packet Forwarding Router Configuration Review

ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Interfaces -By default all serial and Ethernet interfaces are down -To enable an interface use the No Shutdown command

ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  show ip route: –Displays the routing table.  show interfaces: –Shows the status and gives a detailed description of all interfaces on the router.  show interfaces [interface]: –Shows the status and gives a detailed description for a specific interface on the router.  show ip interface brief: –Shows the status of all interfaces in a condensed format. Examining Router Interfaces

ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring an Ethernet Interface Indicates that physically, the connection is good. If you don’t get this message, make sure that the interface is properly connected. Indicates that the Data Link Layer is operational. On LAN interfaces, you do not normally change the Data Link layer parameters.

ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Reading the Routing Table  The interface was configured with IP Address /24.  That makes it a member of the /24 network.  C = directly connected –R1 has an interface that belongs to this network.  The /24 subnet mask for this route is displayed in the line above the actual route.

ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routers Usually Store Network Addresses  Note that the entries in the routing table are the network address of the IP network. –Occasionally, a “host route” (individual host) is entered in the routing table. –The host route is listed with the host’s IP address and a /32 ( ) subnet mask. –The topic of host routes is discussed in another course.

ITE PC v4.0 Chapter 1 9 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Ethernet Interfaces Participate in ARP  A router’s Ethernet interface participates in a LAN network just like any other device on that network.  This means that these interfaces: –Have Layer 2 MAC address. –Are recorded in a device’s ARP Cache. –Issue ARP Requests when needed. –Issue ARP Replies when required.

ITE PC v4.0 Chapter 1 10 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Ethernet Interfaces Participate in ARP  R2 checks its ARP Cache for a matching MAC address for IP Address  If does not exist, R2 will send an ARP Request and PC2 sends an ARP Reply.  R2 uses PC2’s MAC address and IP Address in the frame as the destination MAC and IP addresses.

ITE PC v4.0 Chapter 1 11 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring a Serial Interface  The serial interface will be in the up state only after the other end of the serial link has also been properly configured and activated.

ITE PC v4.0 Chapter 1 12 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring a Serial Interface CAN be different interfaces on different routers. MUST be members of the same network / subnetwork.

ITE PC v4.0 Chapter 1 13 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Examining Serial Interfaces  Physically Connecting a WAN Interface:  Serial interfaces require a clocking signal to control the timing of the interface.  The DCE provides the clock rate.

ITE PC v4.0 Chapter 1 14 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Examining Serial Interfaces -Physically connecting a WAN Interface. -A WAN Physical Layer connection has sides:  Data Circuit-terminating Equipment (DCE) – This is the service provider.  Data Terminal Equipment (DTE) – Typically the router is the DTE device. Router DTE

ITE PC v4.0 Chapter 1 15 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Configuring serial links in a lab environment  One side of a serial connection must be considered a DCE  This requires placing a clocking signal – use the clock rate command.  Example: -R1(config)#interface serial 0/0 -R1(config-if)#clockrate  Serial Interfaces require a clock signal to control the timing of the communcations. Examining Serial Interfaces

ITE PC v4.0 Chapter 1 16 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Examining Serial Interfaces (In the Lab)  The physical link between R1 and R2 is up. –Both ends have been configured correctly with: An IP Address and Subnet Mask The no shutdown command has been issued.  The line protocol is still down. –The serial interface is not receiving a clock signal. –Issue the clock rate command, on the router with the DCE cable.

ITE PC v4.0 Chapter 1 17 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Examining Serial Interfaces (In the Lab)  The show controllers command is useful in determining the DTE/DCE status of a serial link without having to physically check the cables. –If the cable connected to the router is listed as DCE, then the clock rate command must be issued for the interface.

ITE PC v4.0 Chapter 1 18 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Examining Serial Interfaces (In the Lab)  Available clock rates, in bits per second, are 1200, 2400, 9600, 19200, 38400, 56000, 64000, 72000, , , , , , , , and  If a DTE interface is configured with the clock rate command, the IOS disregards it.

ITE PC v4.0 Chapter 1 19 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying the Serial Interface Configuration

ITE PC v4.0 Chapter 1 20 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying the Serial Interface Configuration  If we use the show ip route command again, we can see that the serial link has been added to the routing table.

ITE PC v4.0 Chapter 1 21 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying the Serial Interface Configuration  Although the clock rate command is two words, IOS spells clockrate as a single word in the running configuration and startup configuration files.

ITE PC v4.0 Chapter 1 22 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  When a router only has its interfaces configured & no other routing protocols are configured then: -The routing table contains only the directly connected networks -Only devices on the directly connected networks are reachable

ITE PC v4.0 Chapter 1 23 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  CDP is a powerful network-monitoring and troubleshooting tool.  Cisco proprietary.  Enables you to access a summary of protocol and address information.  Directly connected Cisco devices only. Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 24 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  By default, each Cisco device sends periodic messages to directly connected Cisco devices.  These messages are known as CDP advertisements.  Information gathered from other devices can assist you: –in making network design decisions, troubleshooting, making changes and network discovery. Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 25 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Layer 3 Neighbors: –At Layer 3, routing protocols consider neighbors to be devices that share the same network address space. Cisco Discovery Protocol (CDP) R1 and R2 are neighbors. R2 and R3 are neighbors. R1 and R3 are NOT neighbors.

ITE PC v4.0 Chapter 1 26 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Layer 2 Neighbors: –CDP operates at Layer 2 only. –CDP neighbors are Cisco devices that share the same physical data connection. Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 27 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  CDP Operation ( show cdp neighbors ): –Device ID: The configured host name of the device. –Port identifiers: The name of the local and remote ports that share the physical connection. –Capability: The type of device. –Platform: The hardware platform of the device.  Show cdp neighbors detail command -Useful in determining if an IP address configuration error Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 28 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  CDP Operation ( show cdp neighbors detail ): Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 29 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  CDP Operation: –Disabling CDP: CDP can be a security risk. To disable CDP globally, for the entire device, use the command no cdp run To stop CDP advertisements on a particular interface, use the command no cdp enable Cisco Discovery Protocol (CDP)

ITE PC v4.0 Chapter 1 30 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Routing and Packet Forwarding Static Routes with “Next Hop” Addresses

ITE PC v4.0 Chapter 1 31 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Static routes are commonly used when routing from a network to a stub network.  A manually configured route used when routing from a network to a stub network Purpose and Command Syntax ( ip route ) Stub Network: A network accessed by a single route. Running a dynamic routing protocol between R1 and R2 is a waste of resources.

ITE PC v4.0 Chapter 1 32 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Simpler version of the Syntax: ip route Command OR

ITE PC v4.0 Chapter 1 33 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Simpler Syntax: –ip route [network address] [subnet mask] [ip address | exit interface] –Note: The ip-address parameter is commonly referred to as the next- hop IP address. The next hop IP Address is the IP Address assigned to the interface of the destination router. ip route Command

ITE PC v4.0 Chapter 1 34 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public ip route Command  ip route - Static route command  – Destination network address  Subnet mask of destination network  Serial 0/0/0 interface IP address on R2, which is the "next-hop" to this network

ITE PC v4.0 Chapter 1 35 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  R1 in our chapter topology knows about its directly connected networks. Configuring Static Routes

ITE PC v4.0 Chapter 1 36 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Add a static route to R1 for the LAN on R2. Configuring Static Routes Network Subnet Mask Next-Hop Address / / 24

ITE PC v4.0 Chapter 1 37 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Add a static route to R1 for the LAN on R2. Configuring Static Routes / / 24 BEFOREAFTER

ITE PC v4.0 Chapter 1 38 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Add a static route to R1 for the R2 to R3 WAN Link. Configuring Routes to Two or More Networks / / 24 R1(config)#ip route Network = Subnet Mask = Next Hop Address =

ITE PC v4.0 Chapter 1 39 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Add a static route to R1 for the R3 LAN. Configuring Routes to Two or More Networks / / 24 R1(config)#ip route Network = Subnet Mask = Next Hop Address =

ITE PC v4.0 Chapter 1 40 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring Routes to Two or More Networks BEFORE AFTER

ITE PC v4.0 Chapter 1 41 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring Routes to Two or More Networks  Verifying Static Routes: Probably a good time to save your configuration.

ITE PC v4.0 Chapter 1 42 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routing Table Principles and Static Routes  Alex Zinin’s Routing Table Principles: –Principle 1: Every router makes its decision alone, based on the information it has in its own routing table. –Principle 2: The fact that one router has certain information in its routing table does not mean that other routers have the same information. –Principle 3: Routing information about a path from one network to another does not provide routing information about the reverse, or return, path.

ITE PC v4.0 Chapter 1 43 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Would a ‘ping’ from a PC on the LAN on R1 to a PC on the LAN on R3 work? Routing Table Principles and Static Routes NO…… NO…… According to the principles, each router makes its own decision based on its routing table. There is no return path to R1 from R3.

ITE PC v4.0 Chapter 1 44 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Routing Table Principles and Static Routes

ITE PC v4.0 Chapter 1 45 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying Static Routes

ITE PC v4.0 Chapter 1 46 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Verifying Static Routes

ITE PC v4.0 Chapter 1 47 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Resolving to an Exit Interface  Before any packet is forwarded by a router, the routing table process must determine the exit interface to use to forward the packet.  When the router has to perform multiple lookups in the routing table before forwarding a packet, it is performing a process known as a Recursive Route Lookup. Packet for

ITE PC v4.0 Chapter 1 48 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Exit Interface is Down  Cannot have a route if the exit interface does not exist.  If an interface is manually taken down (shutdown) or a link fails, all routes that are resolved to that interface as the exit interface will be removed from the routing table. BEFORE AFTER

ITE PC v4.0 Chapter 1 49 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Exit Interface is Down  If the interface is manually activated (no shutdown) or the link is restored, the static routes will be reinstated in the routing table. –The ip route commands still exist in the running configuration file. REINSTATED

ITE PC v4.0 Chapter 1 50 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Routing and Packet Forwarding Static Routes with Exit Interfaces

ITE PC v4.0 Chapter 1 51 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring a Static Route with an Exit Interface  An alternative way of configuring static routes is to specify the exit interface instead of the next-hop address.

ITE PC v4.0 Chapter 1 52 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring a Static Route with an Exit Interface  Notice that the entry in the routing table no longer refers to the next-hop IP address but refers directly to the exit interface. –The table lookup will now resolve the route to the same Serial 0/0/0 interface in a single lookup.

ITE PC v4.0 Chapter 1 53 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring a Static Route with an Exit Interface  Also note that the static route displays the route as directly connected.  It is important to understand that this does not mean that this route is a directly connected network or a directly connected route.  This route is still a static route.

ITE PC v4.0 Chapter 1 54 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Modifying Static Routes You have entered this static route and testing fails. OOOPS! That’s the wrong next-hop address!  There is no way to modify a static route. It must be deleted and reconfigured. The no form of the command is used to delete the invalid static route. Re-enter the command line with the proper parameters.

ITE PC v4.0 Chapter 1 55 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Static Routes with Ethernet Interfaces  It is best not to use only an exit interface with Ethernet interfaces.  Since many different devices can be sharing the same multi- access network, the Router will have difficulty determining the destination MAC address.  Use both the exit interface and next-hop address for Ethernet exit interfaces. NOT Recommended Recommended

ITE PC v4.0 Chapter 1 56 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Static Routes with Exit Interfaces  Verifying the Static Route Configuration -Use the following commands  Step 1 show running-config  Step 2 verify static route has been entered correctly  Step 3 show ip route  Step 4 verify route was configured in routing table  Step 5 issue ping command to verify packets can reach destination and that Return path is working

ITE PC v4.0 Chapter 1 57 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Routing and Packet Forwarding Summary and Default Static Routes

ITE PC v4.0 Chapter 1 58 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary Static Routes  Route Summarization: –A summary route is a single route that can be used to represent multiple routes. Generally a set of contiguous networks. Have the same exit interface or next-hop IP address. Creates smaller routing tables More efficient routing table lookup process. FYI As of March 2007, there are more than 200,000 routes in the Internet core routers. Most of these are summarized routes.

ITE PC v4.0 Chapter 1 59 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary Static Routes  R3 has three static routes configured. –All three routes are forwarding traffic out the same Serial 0/0/1 interface. –Can be summarized to / 22 ( )

ITE PC v4.0 Chapter 1 60 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary Static Routes

ITE PC v4.0 Chapter 1 61 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary Static Routes  Any packet with a destination IP address belonging to the /24, /24, or /24 network matches this summarized route. BEFORE AFTER

ITE PC v4.0 Chapter 1 62 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Default Static Routes  A default route is a static route that is used when there are no routes that have a specific match to the destination network.  Default routes are used: –When a router has only one other router to which it is connected. This condition is known as a stub router. ip route [ip address | interface]

ITE PC v4.0 Chapter 1 63 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Default Static Routes A common use for static routes is connecting a company’s edge router to the ISP network. ip route ip route

ITE PC v4.0 Chapter 1 64 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Default Static Routes A common use for static routes is connecting a company’s edge router to the ISP network.

ITE PC v4.0 Chapter 1 65 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Introduction to Routing and Packet Forwarding Managing and Troubleshooting Static Routes IN THE LAB

ITE PC v4.0 Chapter 1 66 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public

ITE PC v4.0 Chapter 1 67 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Purpose of the debug ip routing command  Allows you to view changes that the router performs when adding or removing routes  Example: -R2#debug ip routing -IP routing debugging is on Configuration changes Troubleshooting

ITE PC v4.0 Chapter 1 68 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Purpose of the debug ip routing command –Disable debug ip routing by using either the undebug ip routing command or the undebug all command. Troubleshooting

ITE PC v4.0 Chapter 1 69 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Troubleshooting  Troubleshooting a Missing Route  Tools that can be used to isolate routing problems include: -Ping– tests end to end connectivity -Traceroute– used to discover all of the hops (routers) along the path between 2 points -Show IP route– used to display routing table & ascertain forwarding process -Show ip interface brief- used to show status of router interfaces -Show cdp neighbors detail– used to gather configuration information about directly connected neighbors

ITE PC v4.0 Chapter 1 70 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Solving a Missing Route  Finding a missing or mis-configured route requires methodically using the correct tools -Start with PING. If ping fails then use traceroute to determine where packets are failing to arrive  Issue: show ip route to examine routing table. -If there is a problem with a mis-configured static route remove the static route then reconfigure the new static route Troubleshooting

ITE PC v4.0 Chapter 1 71 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Solving a Missing Route Troubleshooting

ITE PC v4.0 Chapter 1 72 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public  Solving a Missing Route Troubleshooting

ITE PC v4.0 Chapter 1 73 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Routers -Operate at layer 3 -Functions include best path selection & forwarding packets  Connecting Networks WANs Serial cables are connected to router serial ports. In the lab environment clock rates must be configured for DCE LANs Straight through cables or cross over cables are used to connect to fastethernet port. (The type of cable used depends on what devices are being connected)  Cisco Discovery Protocol A layer 2 proprietary protocol Used to discover information about directly connected Cisco devices

ITE PC v4.0 Chapter 1 74 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public Summary  Static Routes -This is a manually configured path that specifies how the router will get to a certain point using a certain path.  Summary static routes -This is several static routes that have been condensed into a single static route.  Default route -It is the route packets use if there is no other possible match for their destination in the routing table.  Forwarding of packets when static route is used -Zinin’s 3 routing principles describe how packets are forwarded  Troubleshooting static routes may require some of the following commands: -Ping -Traceroute -Show IP route -Show ip interface brief -Show cdp neighbors detail

ITE PC v4.0 Chapter 1 75 © 2007 Cisco Systems, Inc. All rights reserved.Cisco Public